1. Field of the Invention
The present general inventive concept generally relates to a multi-input and multi-output device and a tuner for two-way OpenCable. More particularly, the present general inventive concept relates to a splitter and a tuner enabling a two-way communication system of OpenCable and a terrestrial 2 PIP function to be effectively implemented.
2. Description of the Related Art
At the present time, various broadcast media, such as analog over-the-air broadcasts, digital over-the-air broadcasts, analog cable broadcasts, and digital cable broadcasts, broadcast a variety of programs, so that devices connected to an antenna and/or cable are needed to receive different broadcast programs. Thus, a splitter is required to split signals of various formats input through the antenna or cable to corresponding receivers. Furthermore, in general, a multimedia device has a picture-in-picture (PIP) function displaying two screens on one display unit at the same time.
FIG. 1 and FIG. 2 are views illustrating a multi-input and multi-output switching device and a receiver having the same, which are disclosed in the Korean patent publication number of 01-2003-54438.
FIG. 1 is a block diagram illustrating a signal-receiving system using a conventional multi-input and multi-output switching device, and FIG. 2 is a block diagram illustrating a signal-receiving system having a PIP function as shown in FIG. 1. The first input port 21a of the multi-input and multi-output switching part 20 is connected to an antenna for terrestrial waves, and the second input port 21b of the same is connected to cable, the first output port 21c is connected to a tuner 25 for both analog and digital signals, the second output port 21d of the same is connected to the VTR 26, and the loop-through output port 21e of the same is connected to a cable modem or a web box 27.
Thus, the first splitter circuit 22a is connected to the first input port 21a, and splits into two signals an analog or a digital terrestrial broadcast signal past through a low noise amplifier (LNA) 21. The third splitter circuit 22c splits into two signals an input signal, that is, a cable broadcast signal, of the second input port 21b that is applied through the second splitter circuit 22b. The first switching circuit 23 operates according to an external control signal (second voltage), and applies to the first output port 21c one of the first split signal of the first splitter circuit 22a and the first split signal of the third splitter circuit 22c. The second switching circuit 24 operates according to an external control signal (first voltage), and applies to the second output port 21d one of the second split signal of the first splitter circuit 22a and the second split signal of the third splitter circuit 22c. Thus, the first and second output ports 21c and 21d can output a terrestrial broadcast signal or a cable broadcast signal, respectively. That is, signals to be output to the first and second output ports 21c and 21d can be diversely selected depending on the structure of a signal-receiving system.
The loop-through output port 21e is a port used upon two-way communications through cable connected to the second input port 21b, connected to a cable modem or the web box 27. Data input to and output from the loop-through output port 21e has different bands from the cable broadcast signal, so that the data is output to the second input port 21b through the second splitter circuit 22b regardless of the receptions of the cable broadcast signal, and sent to the cable.
Since an RF splitter is needed to implement a PIP function, the RF splitter necessarily selects and outputs either a terrestrial signal or a cable signal to the first output port 21c and the second output port 21d. The tuner connected to the first output port 21c is a sub tuner, and has a compatible tuner 25 generally carrying out the digital (8VSB) and analog (NTSC) functions to implement the 2 PIP since the turner 25 can input a digital signal or an analog signal as an over-the-air broadcast signal. The tuner connected to the second output port 21d has functions capable of processing diverse digital signals for QAM, QPSK, and 8VSB, and a NTSC signal, and operates as a main tuner 30 (refer to FIG. 2).
If a terrestrial waves (a 8VSB digital signal or an NTSC analog signal) are selected and output to the first and second output ports 21c and 21d, four PIPs such as digital-digital, analog-analog, analog-digital, and digital-analog PIPs can be achieved. The electromagnetic field intensity of an over-the-air signal of terrestrial wave can be very low, and, if the electromagnetic field intensity of a signal is very low, the low noise amplifier 21 operates. In general, the low noise amplifier 21 operates only in the over-the-air input mode since the electromagnetic field intensity of a cable signal is appropriate.
If an input signal for cable is output to the first and second output ports 21c and 21d in the same manner, it is configured to carry out fourfold PIPs even in the case that a terrestrial wave is selected at the first output port 21c and a cable signal is selected at the second output port 21d, or, the cable signal is selected at the first output port 21c and the terrestrial wave is selected at the second output port 21d. 
However, the conventional technologies for the above configuration have problems as below.
Since one low noise amplifier 21 is used for the first input port (or over-the-air input port) 21a and an output signal of the low noise amplifier 21 is commonly applied to the first and second output ports 21c and 21d, a sub screen completely disappears and then appears in two seconds every time the channels of the main tuner 30 are changed or scanned, when the tuner 25 is set to a specific channel. In detail, in case of the 2 PIP, in fact, it hardly tells which screen is the main or the sub screen. Thus, the sub screen can be displayed as a small window on the screen, but the screen can be divided in halves to have a dual window. Furthermore, the characteristics of a digital signal cause a screen to completely disappear and then appear after quite a while, that is, in about two seconds, over the extent that the screen momentarily shivers, since the digital channel demodulator operates again in case of failure in locking as well as the MPEG and AC-3 decoding blocks at next stages have to newly process a signal. To overcome the above problems, it can be considered to install the low noise amplifier 21 only on the side of the main tuner 30, but, in this case, the performance of the tuner 25 can be degraded if the electromagnetic field of a signal is weak. That is, in case of the 2 PIP, as stated above, in order to prevent a severe transient state of a digital signal, the tuner is not controlled, but a video signal at rear stages is changed, in the swapping mode of the main and sub screens. In case of the 2 PIP, the tuner is not directly controlled since there are various functions, that is, various swapping functions such as smooth swapping function of main and sub screens, but the video signal at rear stages is switched to each other. However, the low noise amplifier 21 is installed only on the side of the main tuner 30, so that, if the main and sub screens are swapped, the sub tuner 25 having no low noise amplifier (LNA) 21 serves as the main tuner 30 and the main tuner 30 having the low noise amplifier 21 serves as the sub tuner 25. Since the sub tuner 25 having no low noise amplifier 21 serves as the main tuner 30, the performance of the main tuner 30 becomes degraded.
The United States has adopted the one-way OpenCable standards, but the Republic of Korea has adopted the two-way OpenCable standards. The United States are to adopt the two-way OpenCable standards. Thus, in the existing one-way standards, there is no problem in that the OOB RX block 33 receives a signal through the diplexer 31 inside the main tuner 30. On behalf of the Return channel, the main tuner 30 has therein the blocks of OOB RX 33 (receiving signals) and OOB TX 34 (transmitting signals) connected with the diplexer 31 by a cable 36. In the above, the OOB (Out of band) refers to a channel separately providing information on encoding keys, channel modulation modes, and other channel tables. The main tuner is also capable of handling In-Band signals with an In-Band block 32, and the main tuner also has a demodulator 35 capable of processing both OOB and In-Band signals. The two-way OpenCable tuner 30 has the diplexer 31 therein since the existing two-way cable modems are mostly the set-top boxes without consideration of PIP functions. However, in the OpenCable market in the future, if the television sets having a Cable signal-receiving function is compulsorily installed with a CableCARD and has the two-way function instead of the one-way function currently widespread, high-quality television sets with the conventional RF splitter and tuner can not have the two-way function since it is provided with the PIP function. In order to implement the two-way OpenCable, the input port (second splitter circuit 22b of FIG. 1) of the tuner 20 has to be split, so one of the split input ports is used for the In-Band channel and the other of the same is used for the Out-of-Band (OOB). If the RF splitter is used prior to the tuner on behalf of the general PIP function, there occurs a problem of interrupting a path from the signal-receiving stage to the signal-transmitting stage for the OOB return channel since amplifiers of the RF splitter have one-way characteristics. That is, the above prior art has the loop-through output port 21e as a port for two-way communications, but, since the RF splitter supports one-way communications as above, there occurs a problem in that the two-way OpenCable can not be implemented while having the PIP function.
There occurs a problem in the prior art in that the PIP mode using the cable and terrestrial signals can not be implemented due to the interferences of the cable and terrestrial signals in the same channel.